1. Field of the Invention
This invention relates to a motor drive apparatus for a camera and more particularly to a driving circuit and structural arrangement of connecting terminals of the motor drive apparatus (hereinafter called the motor drive unit).
2. Description of the Prior Art
With the advancement of applications of electronics to cameras in recent years, many cameras accomplish film winding and rewinding operations by attachable motor drive units. Each of these motor drive units is provided with electrical connection terminals for signal transmission. The terminals are disposed, in addition to a mechanical driving force transmitting part, between the camera and a cooperating motor drive unit. A shutter release signal, a winding completion signal, etc. are transmitted between the camera and motor drive unit through these terminals. Ordinarily, an attempt to diversify the function of the motor drive unit with an additional facility for switch-over between single shot photographing (hereinafter called S for short) and continuous photographing (hereinafter called C for short) necessitates an increase in the number of signal transmission terminals required.
A cooperating camera and motor drive unit, each having all such signal transmission terminals plus a part for effecting change-over between continuous photographing and single-shot photographing (hereinafter called C-S change-over part), are able to perform a switch-over action between single shot photographing and continuous photographing. The part for effecting change-over may be disposed on the side of the motor drive unit. However, an attempt to use such a motor drive unit that has all such signal transmission terminals in combination with a camera having a lesser number of connection terminals tends to cause various inconveniences such as a short circuit between terminals resulting from bringing some of the terminals on the side of the motor drive unit into contact with a grounded casing or the like disposed on the side of the camera body.
In the accompanying drawings, FIGS. 1A, 1B and 1C show an example of the above. A motor drive unit 1 shown in FIG. 1C is provided with signal transmission terminals T1, T2 and T3. These terminals are arranged to effect circuit connection when brought into contact with faces of signal terminals disposed on the bottom face of the casing of a camera. The motor drive unit 1 is further provided with a C-S change-over operation part S4 for selection between single shot photographing and continuous photographing. When the motor drive unit 1 which has the terminals arranged as described above is attached to a camera 2 having signal terminals TC1, TC2 and TC3 as shown in FIG. 1A, a circuit provided on the side of the motor drive unit and a circuit provided on the side of the camera body are connected to each other through these terminals to effect transmission of a signal. Then, a selecting operation on the switch S4 enables the camera to operate either in a single shot photographing mode or in a continuous photographing mode accordingly.
In the case of a camera 3 shown in FIG. 1B, there are provided only two terminals TC1 and TC2 on the side of the camera body. When the motor drive unit 1 shown in FIG. 1C is attached to the camera body 3, one of the terminals provided on the side of the motor drive unit 1 (for example, the terminal T3) comes into contact with the casing of the camera body to be thus grounded thereby.
With the motor drive unit 1 which is shown in FIG. 1C connected to the camera 2 shown in FIG. 1A, a circuit is formed as shown in FIG. 2. In FIG. 2, the camera body circuit portion is identified by the letter "C" and a motor drive unit circuit portion is identified by the letter "M". The two circuits are connected to each other through a grounding terminal T1, winding signal terminals T2 and a mode signal terminal T3. A circuit block A on the camera side represents a known camera control circuit including a light measuring circuit, a shutter release circuit including an electromagnet and an exposure control circuit. There are provided a power source B' for the camera; a release switch S1 which is turned on when a release button is depressed and is turned off when the button is released from the depressed position; and a winding switch S2 in which the wiper is connected to the terminal b upon completion of a shutter release action, and to another terminal a, upon completion of a film winding action. In the motor drive unit, there are provided a power source battery B; a power source switch S3; a mode switch S4 which performs a switch-over action between single-shot photographing (S) and continuous photographing (C); and a motor M. Transistors Tr.sub.1, Tr.sub.2 and Tr.sub.3 form a control circuit. Reference symbols R.sub.1, R.sub.2 and R.sub.3 indicate resistors and D a diode. The operation of the circuit shown in FIG. 2 is as follows:
Upon completion of film winding, the wiper of switch S2 of circuit C contacts terminal a. Depressing the shutter button closes the switch S1. Assuming that the mode switch S4 on the motor drive unit side M is in the position C for continuous photographing and that the power source switch S3 is on, the transistor Tr.sub.1 is off. Accordingly, transistors Tr.sub.2 and Tr.sub.3 which are provided for driving the motor M, are off. Accordingly, the motor M is not driven. Operation of, the electromagnet provided within the camera control circuit A produces a shutter release action in a known manner. Upon completion of the shutter release action, the switch S2 shifts to the terminal b. The transistor Tr.sub.1 is then biased by the resistor R.sub.2 and turns on. This in turn causes the transistors Tr.sub.2 and Tr.sub.3 to turn on respectively. Accordingly, the motor M rotates to perform a winding action through a film winding system which is not shown. Upon completion of the winding action, the switch S2 shifts to terminal a to bring the motor M to a stop as described above. In that instance, if the release button is continuously depressed, the release switch S1 continues to be closed. Therefore, another shutter release action occurs. Repetition of these operations occurs in continuous photographing. When the shutter button is released from the depressed position, the switch S1 turns off to bring the release action to a stop.
For single shot photographing, the mode change-over switch S4 is shifted to its position S as shown in FIG. 2. In this case, the switch S1 turns on in response to depression of the release button. This causes a release action to take place on the side of the camera. Upon completion of the release action, the switch S2 shifts to the terminal b to cause the transistor Tr.sub.1 to turn on. However, since the collector current of the transistor Tr.sub.1 flows to the terminal T.sub.3 (through the resistor R.sub.3 and the diode D) and is then grounded through the switch S1, the motor driving transistors Tr.sub.2 and Tr.sub.3 are maintained in the off state. Therefore, the motor M does not rotate and no winding action is performed. Then, when the shutter release button is released from the depressed position, the switch S1 turns off. The collector current of the transistor Tr.sub.1 becomes the base current of the transistor Tr.sub.2 to cause the motor driving transistors Tr.sub.2 and Tr.sub.3 to turn on. This in turn causes the motor M to rotate to perform a winding action. Upon completion of the winding action, the switch S2 shifts to the terminal a. Following this, a subsequent depression of the shutter release button again initiates single shot photographing as described above.
Let us now consider a case where the motor drive unit 1 shown in FIG. 1C is attached to the other camera 3 which is provided with only the signal transmission terminals TC1 and TC2 (hereinafter called a camera having a mechanical coupling part of a different type), the terminal T3 shown in FIG. 2 contacts the camera body and the grounding line as indicated by a broken line in FIG. 2. Under this condition, if the mode change-over switch S4 is in the continuous photographing position C, continuous photographing can be accomplished through the actions of the release switch S1 and winding completion switch S2 disposed on the side of the camera body C. When the switch S4 is shifted to the single-shot photographing position S, the switch S2 comes to shift to the terminal b thereof upon completion of a release action. Then, even when the transistor Tr.sub.1 turns on, the base voltage of the driving transistor Tr.sub.2 becomes almost equal to ground potential through the diode D, the switch S4 and the terminal T3. Therefore, the motor M then does not rotate. This construction not only makes the film winding action impossible but also results in wasting much energy of the battery B because the collector current of the transistor Tr.sub.1 continues to flow through the resistor R.sub.3 to the circuit of the diode D, the mode switch S4 and the terminal T3. Thus a motor drive unit of the type, as shown in FIG. 1C, cannot be used for a camera of the type, as shown in FIG. 1B, in the mode S (single shot photographing mode) though it is usable for such a camera in the mode C (continuous photographing mode).